U.S. Pat. No. 5,201,402, assigned to ASGCO Manufacturing, Inc., assignee of the present application, describes a tensioning device for adjusting the contacting force of a scraper blade on an endless conveyor belt. The tensioning device described therein is a rotary tensioner which adjusts the contacting force of the scraper blade on the conveyor belt surface by controlling the torque exerted on a rotatable shaft that supports the scraper blade. To that end a tensioning collar and an adjustment collar are disposed adjacent to one another on the support shaft. The adjustment collar is fixed to and rotates with the support shaft. The tensioning collar is attached to one end of a torsional bias mechanism such as a coil spring. The other end of the bias mechanism is fixed to the conveyor belt frame. Each collar has a series of holes formed therethrough, the holes being arrayed at a selected radial distance from the axis of the support shaft. As the collars are rotated relative to each other, the torsional bias on the support shaft is increased or decreased, and the holes on one collar move into and out-of axial alignment with the holes on the other collar. Each series of holes has different spacing between respective holes so that the torsional bias can be adjusted in very small increments. The collars are locked into relative position by the insertion of a lock-pin through two aligned holes.
Although the known device works well, in practice it was found that adjustment of the torsional bias of the tensioning device requires the efforts of two persons. In the arrangement described in the aforesaid patent, one hand is necessary to rotate the tensioning collar and a second hand is necessary to hold the scraper blade in engagement with the conveyor belt surface by rotating the support shaft. The latter operation is usually performed by rotating the adjustment collar in a direction counter to that of the tensioning collar. A third hand is then necessary to insert the locking pin through the aligned holes in the collars because the first two hands must be used to maintain the two collars in proper alignment.